Sealing of dyed anodized aluminum



fore been almost impossible to eliminate.

' SEALING F DYED ANODIZED ALUMINUM Frank P. Stiller, Glen Rock, N.J., assignor to Sandoz,1 -In c., New York, N.Y., a corporation of New York No Drawing. Application August 26,1957 Serial No. 680,416

10 Claims. (Cl.204-35) The present invention relates to the sealing of dyed an 'odized aluminum.

Dyed anodic coatings on aluminum must be sealed in order to prevent staining, leaching of the dye in water, and possible loss of color by sublimation of the dye. In addition, it has been shown that certain sealing techniques enhance the lightfastness of the dyed coating.

Sealing can be accomplished by impregnating the film r with oils and waxes; by hydrating the aluminum oxide,

which causes an increase in volume thereby closing the pores; or by treatment with hydrolyzable metallic salts such as nickel acetate and cobalt acetate.

The latter I method is the one most commonly used for dyed coatings. i

form a heavy metal complex. However, the hydrolyzable metallic salt sealing treatment is bound up with a serious disadvantage in that, when the film is completely sealed,

'ducing increased lightfastness with dyes which react to I a cloudy coating of basic nickel (or cobalt) acetate is deposited on its surface. coatings dyed with concentrated dye solutions (such as for black work), a residue which appears to be a reaction product of the dye, the aluminum oxide, or impurities contained therein, and the hot water, is also formed. These films are referred to in the trade as smutj While the basic nickel acetate smut can be controlled to some degree by careful regulation of pH, sealing treatment'time and temperature of the sealing bath, the dye smut left on black and other dark shades has hereto- The formation of these smuts necessitates an additional operation in the processing cycle, that of mechanically polishing the surface of the work (commonly referred to as color buffing). This is a costly operation for the anodizer, since each part. requires individual handling and, in addition, there are numerous complicated shapes which are impossible to polish mechanically. A primary object of the present invention is the em .bodiment of a process whereby sealing of dyed anodized aluminum may be accomplished by the hydrolyzable metallic salt sealing treatment but without the formation of smut, whereby the necessity for the aforesaid additional operation for the mechanical elimination of smut is obviated.

This object of the invention is realized by the expedient of incorporating into the sealing bathwhich otherwise consists essentially conventionally of nickel acetate and/ or cobalt acetate in aqueous solution also containing a pH determinant or buffer-a so-called anti-smu agent. As will hereinafter more specifically appear, the anti-smut agent takes the form of a lignosulfonate which may be used in a variety of forms, e.g. simply as straight sulfite waste liquor which has been evaporated to dryness, or in the form of a metal lignosulfonate such as calcium lignosulfonate or sodium lignosulfonate, or most advantageous- In addition, on heavy anodic Patented May 26, .1959

ice

ly in the form of desugared lignosulfonate, preferably desugared calcium lignosulfonate.

The process of the invention has the advantage of being quite uncomplicated. Thus, the aluminum article (and this includes articles of which the exposed surface or surfaces are of aluminum, the remainder of the articles being of desired composition) is anodized (anodically oxidized) and is thereafter dyed in a solution of an appropriate dyestuif, as in current commercial practice.

The dyed article is then subjected to the desired sealing operation by immersion in an aqueous sealing bath which contains the nickel acetate and/or cobalt acetate and a buffer such as boric acid, borates, acetate, or other well known buffering agents. The proportions of these ingredients are widely variable and, generally speaking,

this phase of the procedure may follow the teaching of Tosterud (U.S. Patent No. 2,008,733). The important feature, if the object of the invention is to be realized, is that the sealing bath also contains at least 0.1% by Weight of anti-smut agent; the upper limit of content of this agent is determined solelyby solubility characteristics and economics, any excess can do no harm except that its use may be wasteful.

In marketing the composition according to the invention, it is preferred to have the said composition in the form of a dry mixture, readyfor incorporation into water to form asealing bath. Such a dry composition may, for example, consist of substantially equal parts by weight of nickel acetate, buifering agent (e.g. boric acid), antismut agent (e.g. desugared calcium lignosulfonate), and about /5 part by weight of cobalt acetate. It is preferred to add this to water, when preparing a sealing bath, in a proportion of 16 grams per liter of aqueous bath. The buifer is used so that it determines a pH such that there is no precipitation in the bath of hydroxides of metals due to hydrolysis of the hydrolyzable nickel acetate and/or cobalt acetate. The necessary pHmay be achieved by the addition of further boric acid to the sealing bath if nec essary; it is also possible to establish the appropriate pH by the periodic addition of acetic acid to the sealing bath.

As already mentioned, the result here desired to be achieved involves the presenceof the lignosulfonate molecule. This may be derived from a relatively pure salt, such as calcium lignosulfonate or sodium lignosulfonate or from a relatively impure material such as the product of the evaporation to dryness of ordinary sulfite waste liquor. The preferred material is desugared calcium lignosulfonate which presents the advantage over theundesugared lignosulfonates that, due to the minimum amount of sugar present, it is less subject to decomposition from growth of bacteria mold, and; that a sealing bath made up from a mixture containing this desugared antismut agent requires no adjustment of pH when made up with normally neutral or slightly acidwater.

Sulfite waste liquor which is available in large quantities in the manufacture of sulfite pulp comprises considerable quantities, in some cases up to about 20% of sugar, and processes have been developed whereby these sugar values are effectively utilized for the manufacture of various ultimate products such, for example, as yeast (more especially to be used in the feeding of cattle) and ethyl alcohol. The residue from these processes name- 1y, desugared sulfite waste liquor, consisting essentially of calcium, magnesium, sodium and/ or ammonium lignosulfonates, depending upon the base material used in making the cooking liquoris thus available cheaply and in large quantities. The dry residue is obtainable by evaporation.

The following examples illustrate representative embodiments of the invention, it being understood that the embodiments employing the aforesaid desugared material A homogeneous dry mixture is made up by intimately admixing 2.5 parts of nickel acetate crystals, 0.5 part of cobalt acetate crystals, 2.5 parts of boric acid and 2.5 parts of dry desugared calcium lignosulfonate. The mix ture is stable on storage for long periods of time.

In use, the anodically oxidized and dyed article is immersed in a boiling or substantially boiling sealing bath consisting of the aforesaid mixture in 500 parts by volume of water. The immersion, and concomitant sealing treatment, is continued for about minutes. The resultant sealed, dyed, anodized aluminum does not show any smutty deposit and may be used without supplementary polishing or rubbing.

Example 2 A homogeneous dry mixture is made up by intimately admixing 3.0 parts of nickel acetate crystals, 2.5 parts of boric acid and 2.5 parts of dry desugared calcium lignosulfonate. The mixture is stable on storage for long periods of time.

Example 3 A mixture is made up as per Example 1 or 2, except that the dry desugared calcium lignosulfonate is replaced by a corresponding quantity (about 3.0 parts) of nondesugared calcium lignosulfonate. The mixture is stable on storage, although it is inferior in this respect to the mixture according to the preceding examples.

The mixture is employed after the second paragraph of the latter, whereupon a sealed product is obtained, as precedingly described.

In like manner, another of the hereinbefore-mentioned lignosulfonate molecule-providing materials may be used in lieu of those employed in Examples 1 and 2 and in the first paragraph of the present example, with essential 1y like results. Where the material is desugared, superior stability on storage is achieved.

The treatment time and temperature of operating set forth in the examples may be varied without appreciably prejudicing the final results.

Having thus disclosed the invention, what is claimed is:

1. In the sealing of dyed anodically oxidized aluminum by means of a hydrolyzable metallic salt in an aqueous bath, the improvement which consists of carrying out the sealing operation in the presence in the bath of at least 0.1% by weight of, as sole sulfonate additament, a compound containing the lignosulfonate radical, whereby a smut-free product which requires no mechanical after treatment is obtained.

2. In the sealing of dyed anodically oxidized aluminum by means of a hydrolyzable metallic salt in an aqueous bath, the improvement which consists of carrying out the sealing operation in the presence in the bath of at least 0.1% by weight of calcium lignosulfonate as sole sulfonate additament.

3. In the sealing of dyed anodically oxidized aluminum by means of a hydrolyzable metallic salt in an aqueous bath, the improvement which consists of carrying out the sealing operation in the presence in the bath of at least 0.1% by weight of desugared calcium lignosulfonate as sole sulfonate additament.

4. In the sealing of dyed anodically oxidized aluminum by means of a hydrolyzable metallic salt in an aqueous bath, the improvement which consists of carrying out the sealing operation in the presence in the bath of at least 0.1% by weight of sodium lignosulfonate as sole sulfonate additament.

5. In the sealing of dyed anodically oxidized aluminum by means of a hydrolyzable metallic salt in an aqueous bath, the improvement which consists of carrying out the sealing operation in the presence in the bath of at least 0.1% by weight of dried sulfite waste liquor as sole sulfonate additament.

6. An additive for the production, upon incorporation into water, of a sealing bath for dyed anodically oxidized aluminum, said additive consisting essentially of a dry mixture of substantially equal parts by weight, of hydrolyzable metallic salt and a compound containing thelignosulfonate radical, whereby, upon sealing the aluminum in the said bath, a smut-free product which requires no mechanical aftertreatment is obtained.

7. An additive for the production, upon incorporation into water, of a sealing bath for dyed anodically oxidized aluminum, said additive consisting essentially of a dry mixture of substantially equal parts by weight of (a) at least one member selected from the group consisting of nickel acetate and cobalt acetate, and of (b) calcium lignosulfate.

8. An additive for the production, upon incorpora tion into water, of a sealing bath for dyed anodically oxidized aluminum, said additive consisting essentially of a dry mixture of substantially equal parts by Weight ,of (a) at least one member selected from the group consisting of nickel acetate and cobalt acetate, and of; (b) desugared calcium lignosulfonate.

9. An additive for the production, upon incorporation into water, of a sealing bath for dyed anodically oxidized aluminum, said additive consisting essentially of a dry mixture of substantially equal parts by weight of (a) at least one member selected from the group consisting of nickel acetate and cobalt acetate, and of (b) sodium lignosulfonate. I

10. An additive for the production, upon incorporation into water, of a sealing bath for dyed anodically .oxidized aluminum, said additive consisting essentially of a dry mixture of substantially equal parts by Weight of (a) at least one member selected from the group consisting of nickel acetate and cobalt acetate, and of (b) dried sulfite waste liquor.

References Cited in the file of this patent v UNITED STATES PATENTS Hull et al. Feb. 23, 1943 

1. IN THE SEALING OF DYED ANODICALLY OXIDIZED ALUMINUM BY MEANS OF A HYDROLYZABLE METALLIC SALT IN AN AQUEOUS BATH, THE IMPROVEMENT WHICH CONSISTS OF CARRYING OUT THE SEALING OPERATION IN THE PRESENCE IN THE BATH OF AT LEAST 0.1% BY WEIGHT OF, AS SOLE SULFONATE ADDITAMENT, A COMPOUND CONTAINING THE LIGNOSULFONATE RADICAL, WHEREBY A SMUT-FREE PRODUCT WHICH REQUIRES NO MECHANICAL AFTERTREATMENT IS OBTAINED. 